Refrigeration system with suction line accumulator

ABSTRACT

A refrigerant accumulator in the suction line of a closed refrigeration system, provided with a controllably heated metering tube between the bottom of the accumulator and a downstream point in the suction line, to ensure at least adequate reevaporation of the refrigerant, to eliminate slugging and to return oil to the compressor, particularly during the hot gas defrosting portion of the refrigeration cycle, the heating being effected electrically or by means of hot gas from the compressor.

Unite States Patent Kramer 1 Jan. 25, 1972 [54] REFIRIGERATHGN SYSTEMWITH 3 38; #312; :32; lzfleiftt 8.2752637;

, ea oss SUCTION LKNE ACUMULATOR 2,783,621 3/1957 Staebler et al...62/278 [72] Inventor: Daniel E. Kramer, Yardley, Pa. 3,1 18,287 1/1964Mocey ..62/196 X [73] Assignee: Kramer Trenton Company, Trenton, NJ.Primary Examiner wmiam OD 2 Filed; Sept 17, 19 9 Asristant ExaminerP. D.Ferguson l N 858 749 Al!0rneyNolte and Nolte [21] App 0.:

[57] ABSTRACT [52] U.S.Cl ..62/l97,62/278.62/471, A refrigerantaccumumor in the suction line of a closed 62/472 62/503 refrigerationsystem, provided with a controllably heated me- [5]] Int. Cl ..F25b43/02 i g tube between the bottom of the accumulator and a [58] Field ofSearch ..62/l96, 276, 278, 412,472, downstream Dim in the suction line,to ensure at least P 62/471 197 adequate reevaporation of therefrigerant, to eliminate sluggin and to return oil to the compressor,articularly durg P References cued ing the hot gas defrosting portion ofthe refrigeration cycle, the heating being effected electrically or bymeans of hot gas UNITED STATES PATENTS from the compressor. 14,402 101952 S t ..62/503 X 2 6 l war w 5 Claims, 9 Drawing Figures ACCUMULATORrvom- TOR CONDENSER RECEIVER PAVTENTEB JAN25I972 SHEET 1 [IF 3 k E@(Pfim ART) H o 2 (PRIORART) ACCUMULATOR EVBPGRA- TOR RECEWER INVENTORmu; M1 M11 ATTORNEYS PATENTED JANZS 1972 SHEET 2 [IF 3 R E S N E D N 0 Co T INVENTOR 33M 6. Krwm M W! m ATTORNEYS PATENTEBJMWZ $636,723

sum 3 OF 3 EVAPORATOR QONDENSER INVENTOR l me C. )Owmw mwwfnaw ATTO R NEY-S REFRIGERATION SYSTEM WITH SUCTION LINE ACCUMULATOR Modern positivedisplacement refrigerant compressor technology has generated designswhich provide the maximum in capacity per unit, weight, cost and power.In order to achieve these features the compressors are generallydesigned for relatively high rotative speeds and high bearing loads.Standard rotative speeds for compressors are now 1,725 and 3,400revolutions per minute. At these speeds ingestion of liquids of any sortinto the compressor chamber can cause instantaneous mechanical failures.Liquid entering the cylinders can stem from two sources; liquid oil canenter the cylinders from foaming of the oil in the compressor crankcaseon startup under conditions where liquid refrigerant has condensed ordissolved in the oil during the off-cycle. The other source of liquid isliquid refrigerant in relatively pure form which can return underabnormal conditions through the suction line from the evaporator.

If large quantities of liquid refrigerant enter the compressor, much ofthe refrigerant will be entrained into the cylinders with the vapor andwill cause a condition known as slugging which is accompanied bypounding and knocking sounds and frequently causes instantaneouscompressor damage.

If the liquid refrigerant returns to the compressor in small quantities,but over a long period of time, this liquid refrigerant tends to dilutethe oil, reducing its lubricity and generating a condition of rapidbearing wear under those designed conditions of high rotative speeds andhigh bearing loads to which the compressor is ordinarily exposed. Tohelp guard compressors against either immediate or long range damagecaused by the return of liquid refrigerant through the suction line tothe compressor, more and more compressor manufacturers are presentlyrecommending the use of socalled surge drums or suction accumulatorswhose purpose is to catch the liquid refrigerant returning in large orsmall quantities and prevent this potentially harmful liquid refrigerantfrom reaching the compressor. Because of the new require- .ments forsuction line protection against liquid return to the compressor, manymanufacturers have begun'listing for sale suction accumulators withvarious refrigerant holding capacities and various inlet and outlet linesizes supposedly designed to fit a wide range of systems and refrigerantcharges.

Manufacturers of accumulators are faced with the problem of providingpositive means for the oil, which normally circulates with therefrigerant in refrigeration systems, to be returned to the compressor.If this oil is not returned but is caught or trapped in the suctionaccumulator, the compressor may run out of oil or the accumulatorspotential for holding liquid refrigerant will be diminished.

According to the present invention, there is provided an externalbleeder tube between the accumulator and the suction line together withone or more heaters so positioned, constructed, selected and controlledthat liquid refrigerant flowing through the bleeder tube is completelyreevaporated before it reaches the suction line.

Practical embodiments of the invention are shown in the accompanyingdrawings, wherein:

FIG. 1 represents a vertical section of a known type of suction lineaccumulator;

FIG. 2 represents an elevation of another known type of accumulator,parts being broken away;

FIG. 3 is a diagrammatic view of a refrigerating system embodying theapparatus of the present invention;

FIG. 4 represents a vertical section of a first form of accumulatorembodying the invention;

FIG. 5 represents an elevation of a second form of accumulator;

FIG. 6 is a diagrammatic view of a portion of a refrigeration systemshowing an alternative means for heating the bleed tube;

FIG. 7 is a diagrammatic view of a refrigeration system having means forheating both the bleed tube and the suction line;

FIG. 8 is a diagrammatic view of a portion of a refrigeration systemshowing the use of a thermostatic control for the bleed tube heater, and

FIG. 9 is a detail diagram showing means for ensuring discriminatingfunctioning of the thermostatic control of FIG. 8.

According to FIG. 1, the accumulator 10 is a vertically disposedcylinder having an inlet 11 from the evaporator, opening at 12 into theupper part of the cylinder, and an outlet 13 leading to the compressor,the outlet being connected to a U-shaped trap 14 open at its free end 15to receive evaporated refrigerant and provided with a metering orificeor bleed hole 16 adjacent its bottom.

Since the bleed hole is built-in it must be made large enough to returnthe maximum flow of oil that might be expected. Unfortunately,experience has shown that if the bleed hole is made large enough toreturn the largest quantities of oil which might be pumped by anycompressor, the hole is then so large that excessive amounts ofrefrigerant are allowed to return to the compressor when the accumulatoris partially filled with liquid refrigerant. In addition, laboratorytests and experience have shown that the return of refrigerant and oilflow through the bleed hole is related to the vapor velocity passingthrough the accumulator. Although this efiect would not at first appearto be obvious, the effect was positively determined by quantitativelaboratory tests. An investigation of the cause of this increase inrefrigerant flow through the bleed hole showed that it is caused by thepressure at the inside of the tube in which the bleed hole is locatedbeing much lower than the pressure on the outside. The pressure is lowerinside the tube not only by virtue of the frictional pressure drop lossin the outlet tube, but also the much greater pressure reduction causedby the Bernoulli effect, i.e., the higher the fluid velocity, the lowerthe pressure in that fluid.

All constructions of suction accumulators observed to this date areaffected by this problem which means that the rate of refrigerant flowfrom the body of liquid accumulated in the accumulator into the suctionline is not a constant but a variable. An effort by the presentapplicant to solve this problem is shown in FIG. 2, wherein thehorizontally disposed accumulator 17, having an inlet 18 and outletl9-(corresponding to inlet 11 and outlet 13-15 in FIG. 1) is providedwith an external bleeder tube 20, running from a point 21 at the bottomof the accumulator to a point 22 in the suction line 23. This externalbleeder tube 20 is'so designed and constructed that it can be removedand exchanged for a bleeder of a different diameter.

In addition, the easily serviceable design means that the I bleed tubecan be more closely sized to the actual requirements without any concernthat dirt might plug the bleed tube and permanently destroy theusefulness of the accumulator.

Instead of the bleeder having to be made sufficiently large for theworst situation, the bleeder can be made with an internal bore whichexactly matches the system requirement. Even if an error is made ininitially sizing the bleeder its replaceability makes a size adjustmentan easy matter.

Even though the development of the suction accumulator with external andreplaceable bleed tube constituted a tremendous advancement over thebest previously available ac cumulators, and although the application ofthis accumulator has been satisfactory, all these accumulators hadcertain application limitations. All accumulators had, generally, to beinstalled so that a relatively long run of suction line existed betweenthe outlet of the accumulator and the compressor inlet. In addition, thesuction line had to be exposed to an ambient 32 F. or higher. Thepurpose of requiring this length of suction line maintained at arelatively high ambient was to insure that even the limited amount ofliquid refrigerant that flowed through the calibrated bleeder tube intothe suction line under conditions when floodback into the accumulatoroccurred, was completely evaporated to dryness so that no liquidrefrigerant at all entered the compressor. Under the conditions wherethe accumulator was placed very close to the compressor and/or where avery short suction line was employed, or the suction line was exposed tocold winter ambients, for example -l or 20 F reevaporation of even thesmall amount of liquid refrigerant bled through the bleeder tube couldnot occur and this liquid refrigerant entered the compressor causing oildilution and excessive bearing wear leading to early compressor failure.

In order to make sure that no liquid returns to the compressor, evenwhere the suction line is short and cold as, for instance, where theaccumulator is mounted directly on the compressor chassis, either of twosolutions can be employed. A first possible solution is the provision ofa heat exchanger in the suction line between the accumulator outlet andthe compressor using, for instance, the heat available from the hot gasleaving the compressor discharge to warm the suction vapor leaving theaccumulator and evaporate the liquid mixed with that vapor. This systemhas the drawback that the normally cold suction vapor is heated not onlywhen the ambient surrounding the system is low, as in the winter, butalso when the weather is very hot. Then the suction heat exchangeraggravates potential compressor overheating and reduces compressorcapacity by warming the suction vapor entering the compressor whichmakes the vapor less dense and allows the compressor to pump less witheach rotation of its crankshaft.

As illustrated in FIG. 3, a refrigeration system in which the presentinvention may be embodied includes the evaporator 30 supplied withliquid refrigerant from the condenser 31 and receiver 32 under thecontrol of the expansion valve 33. The compressor 34 supplies gaseousrefrigerant under compression through the line 35 to the condenser,during refrigeration, or through the hot gas defrosting line 36,controlled by solenoid valve 37, directly to the evaporator 30 duringdefrosting.

The accumulator 38 is similar to that shown in FIG. 2, receivingrefrigerant from the evaporator through the line 39 and having an outlet40 opening into the upper part of the accumulator and connecting withthe suction line 41 to the compressor. An external bleeder tube 42,similar to tube 20, leads from the bottom of the accumulator to thesuction line and there is also provided, according to the invention, aheater 43 so positioned and controlled that liquid refrigerant flowingthrough the bleed tube is completely reevaporated before it reaches thesuction line. This construction has the advantage that even strongheating of the bleed tube will have essentially no effect on thetemperature of the vapor entering the compressor. The heater thereforebecomes discriminating in that it only heats liquid refrigerant orperhaps oil leaving the accumulator via the bleed tube but does notexert any heating effect on the suction vapor traversing the accumulatoritself.

Such an accumulator, with heated bleed tube, can be mounted at or nearthe compressor, will allow free return of oil which is trapped in theaccumulator, and yet effects the complete evaporation of liquidrefrigerant traversing the oil flow passage without any heating effecton the suction vapor entering the compressor. This system can be usedfor defrosting of cvaporators even when the compressor, accumulator andother high side components are located in ambients as low as 0' or -l0F. An additional improvement in accumulator design is a modification,shown in FIG. 4, which at least partially offsets the variation inrefrigerant flow through the bleeder which occurs with various vaporvelocities. This improvement constitutes extending the outlet of thebleed tube 44 into the outlet tube 45 and bending this outlet, asindicated at 46, upwards so that a pilot tube effect is generated. Withthis construction the impact pressure of the vapor on the end of thebleed tube opposes the increased pressure difference which higher vaporvelocities generate.

An additional refinement in the design of the bleed tube involves theapplication of heat in such a way as to sharply decrease the rate offlow which occurs through the bleed tube even when the bleed tube is ofa large diameter. H68. 3 and 4 show the basic bleed tube arrangement ofthis invention which pitches uniformly from the bottom of theaccumulator to the outlet tube with or without the pilot effect. FIG.shows the bleed tube 47 modified in the form of a trap 48. Heat isapplied at 49 on the downward flowing side of the trap and separately at50 on the upward flowing side of the trap. The application of heat onthe downward flowing side of the trap generates bubbles whose buoyancytends to offset the pressure differential generated by the vapor flowand by the head of liquid in the accumulator. By the correct applicationof the heat at this point the flow of liquid refrigerant in the bleedtube can be adjusted as required so that the heater 50 on the outwardupflowing leg of the bleed tube can completely evaporate the liquidrefrigerant which succeeds in traversing the downflowing leg. Togetherthe division of heat between the downflowing leg and the upflowing legconstitutes means for externally changing the effective flow capacity ofthe bleed tube without actually modifying its internal construction ordiameter. 7

The bubbling of the refrigerant in the trap is comparable to the vaporlock" efi'ect obtainable in any small tube, including the tube 44 inFIG. 4. When liquid refrigerant moves through a relatively small tube inthe form of a solid column of liquid under a given head the flow of thatliquid is sharply impeded when the stream is heated and thereby assumesthe quality of a mixture of vapor bubbles plus liquid. This impedimentcaused by vapor bubbles in a refrigerant liquid stream moving in a smallbore tube is called vapor lock," and when an adequate amount of heat isapplied to the metering tube it could practically cut off most of theflow of liquid through it. While the application of heat to the meteringtube creates the condition called vapor lock in a refrigerant liquidstream, the application of heat to the metering tube while oil is movingthrough it during normal operation has practically a zero effect on theflow of the oil returning to the compressor during normal operationexcept that the oil becomes warmer and correspondingly less viscous.

Heating of the bleeder tube, as described above, is of particularimportance during defrosting, when some of the refrigerant from theevaporator is most likely to be in liquid form. However, the heaters 43,49, 50-may be kept on continuously, if desired, in order to avoid thenecessity for providing special controls. A suitable setting can bedetermined for any given installation and adjustments, if any, may thenbe on a seasonal basis. During normal operation of the system, forrefrigeration, with little or no liquid entering the accumulator, theheating of the small amounts of vapor passing through the bleeder tubehas a negligible effect on the refrigerant gas flowing to thecompressor, but whenever any liquid does enter the accumulator-duringdefrosting or for any reason' during refrigeration-it is renderedharmless by the use of this invention.

As a practical alternative, heat from the compressor discharge may beused to ensure vaporizing temperatures in the bleed tube. FIG. 6 showsan arrangement in which the accumulator 51 has an outlet 52communicating with the suction line 53 to the compressor 54. The bleedtube 55 (similar to the tubes 42 or 44) is heated by close associationwith the line 56 through which flows a portion of the hot gas which isbypassed around a throttling device 58 in the discharge line 57. Theline 56 and tube 55 may be strapped orsoldered together to ensure heattransfer contact. All parts of the suction line normally tend, withvarying degrees of efiectiveness, to vaporize liquid refrigerant passingtherethrough. If the distance from the evaporator to the compressor orfrom the accumulator to the compressor is short, there would be moreneed for heat in the bleed tube and/or in the suction line than therewould if such distances were longer. Since the discharge line carriesmuch more heat than is needed for ensuring complete vaporization in thesuction line, the line 56 in FIG. 6 may be relatively small and thethrottling device 58 may be either a hand valve, for adjustment asrequired, or an orifice of selected size, to ensure an adequatediversion of hot gas through the line 56, while permitting most of saidgas to follow its normal course to the condenser.

lf the refrigeration system includes provision for hot gas defrosting,the hot gas line can be routed adjacent to the suction line, as shown inH0. 7, where the accumulator 59 with inlet 60, outlet 61 and bleed tube62 is associated with hot gas lines for heating both the bleed tube andthe suction line 63. The compressor discharge line 64 includes a portion65 in heat transfer contact with the bleed tube 62(as in FIG. 6) whilethe hot gas defrost line 66, controlled by solenoid valve 67, issimilarly in heat exchange relation to the suction line 63 throughout asufficient length of said outlet line from the accumulator, to evaporateliquid returning during defrost. This supplementary heating wouldprovide a safety factor in case of excess liquid return from theevaporator to the accumulator, above the vaporizing capacity of themetering tube. Such heating of the suction line would not have theharmful effects of continuous heating, mentioned above, since theheating takes place only during defrosting and the suction line is notheated during normal refrigeration.

Where electric heaters are used they may be arranged to turn on when thecompressor starts and to turn ofi when the compressor stops, as by meansof a relay indicated conventionally at 70, in FIG. 3, associated withthe compressor motor circuit. If consumption of electric power must becontrolled carefully a thermostat may be provided on the suction linenear the compressor inlet to turn on the heater or heaters when thesuction line becomes cold, implying the presence of liquid refrigerant.This would mean that electric heaters might remain dcenergized for longperiods of time, for instance, during warm weather when the accumulator,bleed tube and suction line cooperate inherently to perform theirreevaporating function. In colder weather, however, when the ambientaround the suction line is such that liquid flowing through the bleedtube is not reevaporated, the heater would be turned on.

In FIG. 8 is shown a portion of a system similar to that of FIG. 3 buthaving thermostat 71, with bulb 72 adjacent suction line 73 arranged toopen and close the switch 74 in the circuit of heater 75 (correspondingto heater 43).

The use of a thermostat detecting only the suction line temperature, asa means for ascertaining the presence or absence of liquid, is notalways reliable since liquid refrigerant at a temperature higher thanthe thermostat setting could, under certain circumstances, be presentand could return to the compressor without detection by the thermostat.As an added refinement, to eliminate the possibility just mentioned, asmall cartridge heater 76 (FIG. 9) may be added to the suction line 77adjacent the thermostat bulb 78, or to said bulb itself, in order toensure that the thermostat will react only to the presence of liquid,assuming a setting higher than the temperature of any returning liquid.The cooling ability of liquid refrigerant is about 100 times better thanthat of vapor refrigerant. With liquid refrigerant in the suction linethe bulb of the thermostat is effectively cooled despite the presence ofthe small heater 76, tripping the thermostat and energizing therelatively high voltage heater on the bleed tube. If there is only coldvapor in the line, its cooling effectiveness is insufficient to overcomethe heafing of the bulb by the heater 76 and the bleed tube heater isnot energized. The arrangement just described constitutes a positivemeans for detecting the presence of liquid refrigerant in the suctionline without putting a sensor directly in the flow stream.

What is claimed is:

l. A refrigeration system comprising a compressor, a condenser, anevaporator, and a refrigerant accumulator connected in a closed circuitby lines which includes a suction line from the accumulator to thecompressor and a discharge line from the compressor to the condenser,and a restricted passage extending from the lower portion of theaccumulator to a point in the suction line spaced downstream from theaccumulator, said restricted passage being constituted by a bleed tubeone end of which extends into the suction line and is provided with anopening facing upstream, and means for applying heat to said restrictedpassage.

2. A refrigeration system comprising in a closed circuit, a compressor,a condenser, an expansion valve, an evaporator, an accumulator includinga tank, an inlet, an outlet provided with an extension located below thetank, a conduit residin wholly beneath said tank and mechanicallycoupled to the bottom of the tank and said extension, one end of saidconduit extending into said outlet and being provided with an openingfacing upstream, an electric heater thermally connected to said conduit,and a suction line connecting said extension to the compressor inlet.

3. A refrigeration system comprising in a closed circuit, a compressor,a condenser, an expansion valve, an evaporator, an accumulator includinga tank, an inlet, an outlet provided with an extension located below thetank, a conduit residing wholly beneath said tank and mechanicallycoupled to the bottom of the tank and said extension, a suction lineconnecting said extension to the compressor inlet, said conduit having atrap portion provided with a downward flow side and an upward flow side,a heating means comprising a first electric heater adjacent to thedownward flow side, a second electric heater adjacent to the upward flowside, and means for controlling at least one of said heaters.

4. A refrigeration system comprising in a closed circuit, a compressor,a condenser, an expansion valve, an evaporator, an accumulator includinga tank, an inlet, an outlet provided with an extension located below thetank, a conduit residing wholly beneath said tank and mechanicallycoupled to the bottom of the tank and said extension, an electric heaterthermally connected to said conduit, a thermostat in the circuit of saidelectric heater, said thermostat having a sensing element responsive tochanges in temperature, said sensing element being in thermal contactwith said suction line.

5. A refrigeration system according to claim 4 and which includes aheater coacting with said sensing element.

1. A refrigeration system comprising a compressor, a condenser, anevaporator, and a refrigerant accumulator connected in a closed circuitby lines which includes a suction line from the accumulator to thecompressor and a discharge line from the compressor to the condenser,and a restricted passage extending from the lower portion of theaccumulator to a point in the suction line spaced downstream from theaccumulator, said restricted passage being constituted by a bleed tubeone end of which extends into the suction line and is provided with anopening facing upstream, and means for applying heat to said restrictedpassage.
 2. A refrigeration system comprising in a closed circuit, acompressor, a condenser, an expansion valve, an evaporator, anaccumulator including a tank, an inlet, an outlet provided with anextension located below the tank, a conduit residing wholly beneath saidtank and mechanically coupled to the bottom of the tank and saidextension, one end of said conduit extending into said outlet and beingprovided with an opening facing upstream, an electric heater thermallyconnected to said conduit, and a suction line connecting said extensionto the compressor inlet.
 3. A refrigeration system comprising in aclosed circuit, a compressor, a condenser, an expansion valve, anevaporator, an accumulator including a tank, an inlet, an outletprovided with an extension located below the tank, a conduit residingwholly beneath said tank and mechanically coupled to the bottom of thetank and said extension, a suction line connecting said extension to thecompressor inlet, said conduit having a trap portion provided with adownward flow side and an upward flow side, a heating means comprising afirst electric heater adjacent to the downward flow side, a secondelectric heater adjacent to the upward flow side, and means forcontrolling at least one of said heaters.
 4. A refrigeration systemcomprising in a closed circuit, a compressor, a condenser, an expansionvalve, an evaporator, an accumulator including a tank, an inlet, anoutlet provided with an extension located below the tank, a conduitresiding wholly beneath said tank and mechanically coupled to the bottomof the tank and said extension, an electric heater thermally connectedto said conduit, a thermostat in the circuit of said electric heater,said thermostat having a sensing element responsive to changes intemperature, said sensing element being in thermal contact with saidsuction line.
 5. A refrigeration system according to claim 4 and whichincludes a heater coacting with said sensing element.